X-ray films are at present commercially available in a number of types according to image characteristic of the portions or the body to be photographed (or X-rayed) or the photographing purposes. For example, in the case of KONICA CORPORATION, products are already on the market in a number of types such as SR-G for general purpose, SR-V for high-speed purpose as in contrast photographing, SR-H or SR-HG for high-contrast photographing, SR-L for low-contrast photographing as in the photographing of the digestive organs, SR-C for wide-latitude photographing for the photographing of the chest, and also new-CM for the photographing of portions for which an ultra-high sharpness is needed as in the photographing of the breast.
Thus, a number of film types are made for use depending on the individual photographing purposes. This not only makes the stock management by users very cumbersome but also provides a possibility of mistaking film types when used. When the wrong film type is used, the result can be serious difficulty in diagnosis.
From the standpoint of film manufacturers and dealers, it is not preferable to manufacture and sell so many types of films, because of an increase in cost and a difficulty that may be caused in distribution of goods. Thus, improvements therefor have been earnestly sought.
The terms used to define the invention to have their conventional means. The term "fog" as used herein means the density of photographic material after development, measured through a portion of photographic material displaying minimum density. In negative X-ray image, this means the density at unexposed area. In positive X-ray image, this means the density at fully exposed area. The term "characteristic curve" refer to a plot of a density measured on a developed photographic light sensitive material versus exposure.